Ultraviolet curable silicone coating compositions

ABSTRACT

Epoxy functional diorganosiloxane fluids are combined with bis-aryl iodonium salts, particularly linear alkylate bis-dodecylphenyl iodonium salts to form a silicone coating composition effective for rendering surfaces non-adherent to other surfaces which would normally adhere thereto, and which will cure to a final non-adherent state upon brief exposure to ultraviolet radiation. Adhesion of the silicone coating to a substrate can be improved with the addition of β-(3,4-epoxycyclohexyl)ethyltrimethoxy silane.

This application is a division, of application Ser. No. 63,648, filedAug. 3, 1979, now U.S. Pat. No. 4,279,717.

BACKGROUND OF THE INVENTION

This invention relates to improved ultraviolet curable silicone coatingcompositions. More particularly, it relates to pre-crosslinked epoxyfunctional polydiorganosiloxane silicone fluids which are effectivelycured by ultraviolet radiation in the presence of certain linearalkylate iodonium salts. These UV curable silicone coating compositionsare particularly well suited for paper release applications.

Silicone compositions have long been used for rendering surfacesnon-adherent to materials which would normally adhere thereto. For along time, it was necessary that these silicone coatings be applied as adispersion within a solvent in order to control the viscosity of thecoating material so as to be suitable for coating applications. However,although the solvent aids in the application of the coating, it is ahighly inefficient process inasmuch as the solvent must thereafter beevaporated. The evaporation of solvent requires large expenditures ofenergy. Additionally, pollution abatement procedures require thatsolvent vapors be prevented from escaping into the air. Removal andrecovery of all the solvent entail considerable expenditure forapparatus and energy.

Thus, it has been noted that there is a need to provide a solventlesscoating composition which will, however, remain easy to apply to thesubstrate. Such solventless coating compositions are sometimes referredto as "100% solids" compositions. The absence of solvent in suchcompositions lowers the amount of energy required to effect a cure andeliminates the need for expensive pollution abatement equipment. Thepresent invention provides a solventless pre-crosslinked epoxyfunctional polydiorganosiloxane fluid which will cure to a non-adherentsurface when combined with an effective amount of a linear alkylatediaryl iodonium salt and exposed to ultraviolet radiation.

Release coatings are useful for many applications whenever it isnecessary to provide a surface or material which is relativelynon-adherent to other materials which would normally adere thereto.Silicone paper release compositions are widely used as coatings whichrelease pressure-sensitive adhesives for labels, decorative laminates,tranfer tapes, etc. Silicone release coatings on paper, polyethylene,Mylar and other such substrates are also useful as non-stick surfacesfor food handling and industrial packaging applications.

For example, when labels are coated with an adhesive, it is desirablethat the paper backing be easily peeled away from the label when it isready for use, yet the adhesive quality of the label should not bederogated by the fact that it has been peeled away from the substrateupon which it was stored. The same principle applies to certain types ofadhesive tapes which come in rolls. It is necessary that the tape unrolleasily and still maintain its adhesive characteristics. This can beaccomplished by coating the non-adhesive side of the tape with asilicone release composition which will come into contact with theadhesive as the roll of tape is manufactured.

Silicone release compositions are often sold as dispersions of reactivepolysiloxanes in organic solvents such as toluene, or as emulsions inwater. A cross-linking catalyst, also known as the curing agent, is thenadded to the polysiloxane-solvent mixture. The coating composition isapplied to a substrate which is passed through an oven to evaporate thecarrier fluid and cure the silicone to an non-adherent or "abhesive"surface. As noted above, this process is quite energy intensive since itrequires high oven temperatures to evaporate the solvent and effect thecure at commercially useful speeds.

Use of these solvent based products is becoming increasinglyunattractive because of rising energy costs and stringent regulation ofsolvent emissions into the atmosphere. Other solventless siliconerelease compositions such as that described in copending U.S.application, Ser. No. 40,015, filed May 17, 1979, now U.S. Pat. No.4,256,870, and which is assigned to the same assignee of the presentinvention, have addressed the enivronmental problem of hydrocarbonemission but still require high oven temperatures for proper cure.

Optimum energy savings as well as necessary ecological considerationsare both served by radiation curable compositions. Specifically, anultraviolet (UV) radiation curable 100% solids silicone release systemeliminates the need for high oven temperatures and for expensive solventrecovery systems, and is, therefore, a useful and commercially desirableproduct.

UV curable silicone compositions are not unknown. A patent issued to R.V. Viventi, U.S. Pat. No. 3,816,282, June 11, 1974, and assigned to theGeneral Electric Company, describes a room temperature vulcanizablesilicone composition (RTV) in which mercaptoalkyl substituents attachedto polysiloxanes add to vinyl functional siloxanes in a free-radicalprocess upon UV irradiation in the presence of free-radical typephotosensitizers. The particular compositions described by Viventi curetoo slowly to be useful for paper release applications. Furthermore, theuse of mercaptoalkyl photoreactive substituents gives rise to offensiveodors both in product manufacture and in cured materials.

Ultraviolet radiation will initiate free-radical cross-linking in thepresence of common photosensitizers which are well-known to personsfamiliar with the art of radiation curing mechanisms. However, siliconecompositions which utilize photosensitizers (such as benzophenone) as acuring agent also require stabilizers (such as hydroquinone) to preventpremature reaction and provide reasonable shelf-life.

Commonly available photosensitizers are only slightly soluble inpolydimethylsiloxane fluids which are the basic starting materials forsilicone coating compositions. Low solubility causes problems inselection of these necessary ingredients. A further difficulty inherentin free-radical systems is oxygen inhibition which necessitates that thecoated substrates be under an inert atmosphere while undergoingirradiation in order to cure within a reasonable amount of time. Use ofan inert atmosphere adds complication and expense to the coating andcuring process.

It has now been discovered that UV curable epoxy functional siliconeswhich are suitable for release coating applications fall into a narrowrange of epoxy content and viscosity. The limits to these parameters areimposed by the necessity of coating 0.1 to 0.3 mil layers of thesesilicone fluids onto various substrates, and by the necessity for theseformulations to cure quickly upon exposure to UV radiation and whileadhering well to the substrate.

The requirement that these epoxy functional silicones be applied in thincoats dictates that the fluids be of low viscosity such as, for example,approximately 500 to 25,000 centistokes. Consequently, the epoxyfunctional silicones must be low molecular weight fluids. Also, theefficiency of the curing catalyst must be high in order to providesufficient cross-linking and the formation of a tight, smear-resistantcoating which adheres well to the substrate.

The requirement for a highly efficient photo initiator severelyrestricts the structure of the catalyst since it also must be capable ofdissolving or dispersing well in the epoxy functional silicone fluid.Copending U.S. application Ser. No. 974,497, filed Dec. 29, 1978, nowabandoned, by J. V. Crivello, which is assigned to the same assignee asthe present invention, discloses a UV initiated cationic ring-openingcuring mechanism for dimethyl epoxy chainstopped linearpolydimethylsiloxane fluids utilizing bis-aryliodonium salts of thefollowing formula, ##STR1## wherein X=SbF₆, AsF₆, PF₆, or BF₄ andwherein R is a C.sub.(4-20) organo radical selected from alkyl andhaloalkyl and mixtures thereof and n is a whole number equal to 1 to 5,inclusive. The catalysts described by the Crivello application arethick, high viscosity liquids or waxy solids which disperse poorly inlow molecular weight epoxy functional silicones utilized by the presentinvention. These catalysts exhibit typical solubility characteristics ofdiaryliodonium salts, namely, being soluble in polar organic solventssuch as chloroform and acetone but insoluble in non-polar organicsolvents such as pentane, hexane and petroleum ether. Such solubilitybehavior severely limits the utility of these salts for initiating therapid photocuring of epoxy functional silicone paper releasecompositions.

Although Crivello discloses that R may equal organo radicals selectedfrom alkyl, haloalkyl and branched alkyl groups containing from 4 to 20carbon atoms, he did not appreciate the unique characteristics of"linear alkylate" bis(dodecylphenyl) iodonium salts such as aredisclosed by the present invention. These bis(dodecylphenyl) iodoniumsalts will rapidly dissolve in the polysiloxane base polymer fluid anddisperse throughout, thereby being an efficient photo initiator agent.Such salts are particularly well adapted for use with the novel epoxyfunctional silicone coating compositions herein provided.

Epoxy functional silicone paper release coating compositions mustordinarily have epoxy contents of less than approximately 12 weightpercent because of the end uses to which such coating will be put,namely, to serve as non-adherent surfaces capable of releasingaggressive pressure sensitive adhesives. When the epoxy content of thesilicone compositions is greater than about 12 weight percent, excessiveforce is required to remove adhesive coated articles from the curedsilicone coatings. Note, however, that this may be a usefulcharacteristic whenever it is desirable to selectively control therelease characteristics of an adhesive.

It is therefore an object of the present invention to provide novelepoxy functional silicone fluids.

It is another object of the present invention to provide ultravioletlight curable epoxy functional silicone coating compositions.

Another object is to provide silicone coating compositions which exhibitimproved adhesion to substrates upon which they are applied.

It is another object of the present invention to provide a process forpreparing epoxy functional silicone coating compositions.

It is another object of the present invention to provide a method forrendering surfaces non-adherent to materials which would normally adherethereto.

It is another object of the present invention to provide products withnon-adherent surfaces of ultraviolet curable epoxy functional siliconecoatings.

These and other objects of the present invention will become apparent tothose skilled in the art upon consideration of the following detaileddescription of the invention.

SUMMARY OF THE INVENTION

The epoxy functional polydiorganosiloxane silicone fluids provided bythe present invention are more specifically dialkylepoxy chainstoppedpolydialkyl-alkylepoxysiloxane copolymers wherein the polysiloxane unitscontain lower alkyl substituents, notably, methyl groups. The epoxyfunctionality is obtained when certain of the hydrogen atoms on thepolysiloxane chain of a polydimethyl-methylhydrogensiloxane copolymerare reacted in a hydrosilation addition reaction with other organicmolecules which contain both ethylenic unsaturation and epoxidefunctionality. Ethylenically unsaturated species will add to apolyhydroalkylsiloxane to form a copolymer in the presence of catalyticamounts of platinum-metal. Such a reaction is the cure mechanism forother silicone compositions, however, in the present invention, acontrolled amount of this cross-linking is permitted to take place in asilicone precursor fluid or intermediate, and this is referred to as"pre-crosslinking." Pre-crosslinking of the precursor silicone fluidmeans that there has been partial cross-linking or cure of thecomposition and offers the advantages to the present invention ofenabling swift ultraviolet light initiated cure with little expense forenergy and with the elimination of the need for a solvent.

The ultraviolet curable epoxy functional silicone intermediate fluidcomprises a pre-crosslinked epoxy functional dialkyl epoxy chainstoppedpolydialkyl-alkyl epoxy siloxane copolymer silicone fluid which is thereaction product of a vinyl- or allylic-functional epoxide and a vinylfunctional siloxane cross-linking fluid having a viscosity ofapproximately 1 to 100,000 centipoise at 25° C. with a hydrogenfunctional siloxane precursor fluid having a viscosity of approximately1 to 10,000 centipoise at 25° C. in the presence of an effective amountof precious metal catalyst for facilitating an addition curehydrosilation reaction between the vinyl functional cross-linking fluid,vinyl functional epoxide, and hydrogen functional siloxane precursorfluid.

The vinyl- or allylic-functional epoxide may be a cycloaliphatic epoxycompound such as 4-vinylcyclohexeneoxide, vinylnorbornenemonoxide, anddicyclopentadienemonoxide.

The precious metal catalyst can be selected from the group ofplatinum-metal complexes which includes complexes of ruthenium, rhodium,palladium, osmium, iridium and platinum.

The vinyl functional siloxane cross-linking fluid can be selected fromthe group consisting of dimethylvinyl chain-stopped linearpolydimethylsiloxane, dimethylvinyl chain-stoppedpolydimethyl-methylvinyl siloxane copolymer,tetravinyltetramethylcyclotetrasiloxane andtetramethyldivinyldisiloxane. The hydrogen functional siloxane precursorfluid can be selected from the group consisting oftetrahydrotetramethylcyclotetrasiloxane, dimethylhydrogen chain-stoppedlinear polydimethylsiloxane, dimethylhydrogen chain-stoppedpolydimethyl-methyl-hydrogen siloxane copolymer andtetramethyldihydrodisiloxane.

When the above-described pre-crosslinked epoxy functional siliconeintermediate fluids are combined with an appropriate bis-aryl iodoniumsalt, an ultraviolet light cure reaction can be initiated in order toform a final product such as a solventless silicone release coating. Theadhesion of these compositions to a substrate can be improved with theaddition of a small amount of β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

The UV curable epoxy functional silicone compositions of the presentinvention can then be applied to cellulosic and other substratesincluding paper, metal, foil, glass, PEK paper, SCK paper, andpolyethylene, polypropylene and polyester films. A UV initiated reactionwill cure the epoxy functional silicone compositions of the presentinvention and form a non-adherent, abhesion surface on the coatedsubstrate.

When this pre-cross-linked epoxy functional silicone intermediate fluidis combined with an appropriate bis-aryl iodonium salt, an ultravioletcure reaction can be initiated in order to form a final product such assolventless silicone release coating.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Ultraviolet light curable silicone coating compositions of the presentinvention are obtained by combining an iodonium salt which is effectivefor catalyzing an ultravilet light initiated cure reaction of thesilicone coating composition, with a pre-crosslinked dialkyl epoxychain-stopped polydialkyl-alkyl epoxy siloxane silicone fluid having aviscosity of approximately 10 to 10,000 centipoise at 25° C.

The preferred UV-light initiator utilized by the present invention is adiaryl iodonium salt derived from "linear alkylate" dodecylbenzene. Suchsalts have the following general formula, ##STR2## wherein X equalsSbF₆, AsF₆, PF₆, or BF₄. These bis(4-dodecylphenyl)iodonium salts arevery effective initiators for the UV cure of a wide range of epoxyfunctional silicones.

"Linear alkylate" dodecylbenzene is known commercially and is preparedby Friedel-Craft alkylation of benzene with a C₁₁ -C₁₃ α-olefin cut.Consequently, the alkylate contains a preponderance of branched chaindodecylbenzene, but there may, in fact, be large amounts of otherisomers of dodecylbenzene such as ethyldecylbenzene, plus isomers ofundecylbenzene, tridecylbenzene and etc. Note, however, that such amixture is responsible for the dispersive character of the linearalkylate derived catalyst and is an aid in keeping the material fluid.These catalysts are free-flowing viscous fluids at room temperature.

These new bis-dodecylphenyl iodonium salts (II) are profoundly differentfrom previously characterized diaryliodonium salts (I). They are bothpentane-soluble and water-insoluble. The improvements in solubility andcatalytic efficiency of these branched chain substituted salts arefurther underscored by comparison with analogous salts prepared fromstraight chain n-tridecylbenzene and n-dodecylbenzene. Two examples ofthese salts include bis(4-n-tridecylphenyl)iodonium hexafluoroantimonateand bis(4-n-dodecylphenyl)iodonium hexafluoroantimonate which have longlinear hydrocarbon chains. These salts (I), in contrast to the new salts(II), are waxy solids which are neither pentane nor water-soluble, andwhich disperse very poorly in the epoxy functional silicones utilized bythe coating compositions of the present invention. These catalystsafford very sluggish UV cures when utilized for release coatings.

The UV curable silicone coating compositions of the present inventionutilize novel epoxy functional silicone fluids which can be prepared inseveral ways. Epoxy compounds such as 4-vinylcyclohexeneoxide, depictedby the following formula, ##STR3## can be combined with Si-H functionalpolysiloxanes. An addition cure reaction also known as a hydrosilationcan take place between the vinyl functional groups and the Si-H groups.It should be understood that the silicone coating composition undegoesan amount of "pre-crosslinking" before the UV catalyst is added to thecomposition. Pre-crosslinking refers to the ability of the Si-Hfunctional groups to react with the vinyl groups ofdimethylvinyl-stopped linear polydimethylsiloxane fluids, or of othervinyl-containing polysiloxanes, and it serves the useful purpose ofproviding a composition which can be cured to its final abhesive statewith the expenditure of much less energy than would be needed for acomposition that is not so pre-crosslinked.

In other words, ordinary silicone coating compositions require largeexpenditures of energy such as high oven temperatures, in order to curethe product to a final condition. However, the present inventionutilizes an intermediate epoxy functional fluid which has alreadyundergone an amount of pre-crosslinking or hydrosilation such that onlysmall amounts of UV radiation will be necessary to cure it to its finalstate in the presence of the iodonium salt initiators also providedherein.

The epoxy functional silicones can be prepared from other vinyl orallylic-functional epoxy compounds containing olefinic moieties such asallylglycidylether or glycidyl acrylate, vinylnorbornene monoxide anddicyclopentadiene monoxide. Although cyclohexyl epoxy compounds areparticularly useful, other vinyl-functional cycloaliphatic epoxycompounds may be used without significantly altering the properties ofthe product. The scope of the invention is not limited to the4-vinylcyclohexeneoxide species used in the examples.

The epoxy functional polysiloxane intermediate fluids can be prepared inany of several ways. The following examples illustrate several of thesemethods but it must be understood that the present invention is notlimited by these examples. Those skilled in the art will be able toprovide other epoxy functional silicone intermediate fluids uponconsideration of these examples.

EXAMPLE 1

470 grams of a dimethylvinyl chain-stopped linear polydimethylsiloxanefluid having an average molecular weight of 62,000 was mixed with 54grams of 4-vinylcyclohexeneoxide and 0.2 grams Lamoreaux catalyst (H₂PtCl₆ in octyl alcohol) which is described in U.S. Pat. No. 3,220,972,issued Nov. 30, 1965, and assigned to the same assignee as the presentinvention. These materials were dissolved in 550 grams hexane, then 30grams of tetramethylcyclotetrasiloxane (MeHSiO)₄ were slowly added tothe above solution. The complete mixture was refluxed at 70° C. forthree hours. The hexane solvent was stripped off at 60° C. under vacuum,providing a hazy fluid having a viscosity of 875 centipoise as the epoxyfunctional pre-crosslinked silicone product.

EXAMPLE 2

300 grams of a dimethyl hydrogen chain-stopped linearpolydimethylsiloxane fluid of average molecular weight 6,000 wascombined with 0.2 grams Lamoreaux platinum catalyst and was dissolved in200 grams hexane. A mixture of 4.2 grams oftetravinyltetramethylcyclotetrasiloxane (MeViSiO)₄ and 7.6 grams of4-vinylcyclohexeneoxide were added dropwise to the stirring solution.The complete reaction mixture was refluxed at 70° C. for two hours. Uponstripping off the solvent, the epoxy functional silicone intermediatewas a clear amber fluid with a viscosity of 800 centipoise.

EXAMPLE 3

An epoxy functional silicone fluid with improved shelf-life andperformance as compared to Examples 1 and 2, can be provided bycombining 18.8 grams of 4-vinylcyclohexeneoxide with 0.05 grams platimumcatalyst and 7.0 grams of a dimethylvinyl chain-stoppedpolydimethylmethylvinylsiloxane copolymer containing 6.4% methyl-vinylsubstitution and a viscosity of 100 centipoise. These materials weredissolved in 300 grams hexane in a 2-liter flask to which was added 300grams of a dimethyl hydrogen chain-stopped polydimethyl-methyl hydrogensiloxane copolymer containing a total of 2.85% Si-H units and aviscosity of 100 centipoise. This fluid was slowly added to the stirringhexane solution over a 90 minute period. When this addition wascompleted the reaction mixture was refluxed at 70° C. for eight hours.3.0 grams of 1-octene were added to the reaction mixture at this timeand refluxing was resumed for 18 hours. The hexane solvent was strippedoff as described above and a clear product having a viscosity of 380centipoise remained which contained a 5.8% epoxy content in the form of4-vinylcyclohexaneoxide. Infrared analysis of the product detected tofree MeH remaining since the 1-octene acts as an effective scavengingagent.

EXAMPLE 4

Dissolved into a two-liter flask containing 300 grams hexane were 11.0grams 4-vinylcyclohexeneoxide and 0.05 grams platinum catalyst alongwith 15 grams of the vinyl-functional fluid described in Example 3,above. To this mixture was added 300 grams of a dimethyl hydrogenchain-stopped polydimethyl-methylhydrogensiloxane copolymer with aviscosity of 125 centipoise and which contained 1.75% methylhydrogenunits. This mixture was then slowly added to the stirring hexanesolution over a 30 minute period and the reaction mixture was refluxedat 70° C. for 8 hours. At this point, 0.2% MeH was detected as beingunreacted so 6 grams of 1-hexene was added as a scavenging agent and thereflux was resumed for an additional 16 hours whereupon no unreacted MeHcould be detected. The solvent was removed and a clear fluid product of312 centipoise viscosity containing 3.4 weight percent epoxy in the formof 4-vinylcyclohexeneoxide remained.

It is desirable to have as little an amount of unreacted Si-H functionalgroups as possible in the final product because these Si-H functionalfluids will rapidly age to a gel upon exposure to atmospheric moisturein the presence of catalytic amounts of platinum. By adding a smallamount of a low boiling normal alkene such as the octene and hexene, asdescribed in Examples 3 and 4 above, during the hydrosilation thesealkenes act as MeH scavengers and reduce the unreacted MeH to anundetectable range without otherwise affecting the product. Excessalkene is then easily removed during the solvent stripping process.

The above examples are a limited demonstration of the scope andversatility of the epoxy silicone synthesis developed in the course ofthe present invention. It has been found that the addition of smallamounts of vinyl functional dimethylsilicone fluids to the vinyl epoxideduring the hydrosilation of the hydrogen functional precursor fluids notonly provides the pre-crosslinking essential for proper performance ofthe product but also is an effective way to control the viscosity of theabove-described epoxy functional silicone intermediate fluids.

The epoxy functional silicone coating composition of the presentinvention is cured to its final abhesive state with an effective amountof ultraviolet radiation. In order to effect such a cure, a cationic UVcatalyst is incorported into the epoxy functional fluid. For thepurposes of the present invention, it has been found that abis-aryliodonium salt containing a linear alkylate dodecyl substituentis a very effective UV initiator. Particularly effective, for example,is bis(4-dodecylphenyl)iodonium hexafluoroantimonate having formula (II)which can be synthesized in the following fashion. A two literthree-necked round bottom flask was fitted with a mechanical stirrer, athermometer, a nitrogen inlet and a pressure equalizing addition funnel.To this reaction vessel was added approximately 100 parts by weightlinear alkylate dodecylbenzene. To this was added approximately 30 to 60parts by weight of potassium iodate and approximately 60 to 100 parts byweight of acetic anhydride as well as approximately 150 to 200 parts byweight glacial acetic acid. The mixture within the reaction vessel iscontinuously stirred and cooled to a temperature of approximately -10°C. to +10° C. A dry ice acetone bath is effective for reducing thetemperature. Approximately 80 to 120 parts by weight of an acid solutionis added to the contents of the reaction vessel to form a reactionmixture. The acid solution can be a mixture of concentrated sulphuricacid and additional glacial acetic acid. The acid solution may comprisea mixture of approximately 12% to 60% by weight of concentratedsulphuric acid and approximately 40% to 80% by weight glacial aceticacid. This acid solution is added to the reaction mixture at a rateeffective for maintaining the reaction mixture temperature atapproximately -5° C. to +5° C. After completion of the addition, a thickorange slurry is obtained and this reaction mixture can be slowlystirred for approximately 2 to 4 hours at near 0° C. The reactionmixture is then allowed to slowly warm to approximately 20° C. to 30° C.and the stirring is continued for approximately 8 to 15 hours.

As the temperature of the reaction mixture approaches 20° C. moderateexothermic reactions may occur but these can be quickly controlled byreimersing the reaction vessel into the cooling bath. The reactionmixture is then diluted with approximately 500 to 1,000 parts by weightof water and to this stirred mixture was added approximately 5 to 10parts by weight sodium bisulfate or another Group Ia or Group IIa metalbisulfate.

Approximately 30 to 60 parts by weight of sodium hexafluoroantimonate isadded to the reaction mixture. To this mixture is added approximately100 to 150 parts of pentane and the mixture is stirred in the dark forapproximately 2 to 4 hours. The aqueous and non-aqueous layers are thenseparated. A separatory funnel may be used. After separation, theaqueous layer can be further extracted with additional pentane. Thepentane extracts are then combined with the non-aqueous layer and thismixture is washed with fresh water and then concentrated in a vacuum toafford a reddish-brown oil. This oil is then stored in the dark. Thisoil is an approximately 50% pure reaction mixture ofbis(4-dodecylphenyl)iodonium hexafluoroantimonate. Although synthesis bythe above-described method provides a bis-aryl iodonium salt which isonly about 50% pure, nevertheless, the salt is quite effective forinitiating an ultraviolet cure reaction of the epoxy functional siliconecoating composition of the present invention and further purification,while useful, is not required.

Of course, other effective UV initiator salts having formula (II) may beprovided by minor substitutions in the synthesis procedure. For example,the sodium hexafluoroantimonate can be substituted with salts containingAsF₆, PF₆, or BF₄ in order to provide a UV initiator having formula(II).

EXAMPLE 5

Initial cure studies were conducted in the following fashion. Epoxyfunctional silicones were prepared as described above for Examples 1 and2 and were treated with 2% by weight of a cationic UV catalyst salthaving formula (II) by thoroughly mixing the two substances. Theefficacy of the UV catalysts designated by formula (II) as compared tothe UV catalysts designated by formula (I) can be seen in Table 1. Foreach trial listed in Table 1, the heading "Synthesis" denotes the mannerin which the epoxy functional precursor fluid utilized was prepared. Theheading "Weight % Epoxy" refers to the weight percent of epoxyfunctionality in the chosen epoxy functional silicone fluid. Thecomplete mixtures of epoxy functional silicone fluids and UV catalystsalts were then coated onto glass slides in layers of approximately 2mils. The coatings were exposed to a single GE H3T7 medium pressuremercury arc lamp mounted a distance of 5 inches from the sample. Thesamples were all radiated in ambient atmosphere since inert blanketingis not required for this cure system. The expression "Cure" in thefollowing table is defined as the formation of a tack-free solidcoating.

                  TABLE 1                                                         ______________________________________                                                 Vis-  Wt. %   UV Catalyst and Cure Time                              Trial                                                                              Synthesis cosity  Epoxy (I)      (II)                                    ______________________________________                                        A    Example 1 875 cps 9.75  slight gelation                                                                        cure, 10 sec                                                         after 10 sec.                                    B    Example 2 100 cps 3.8   no cure, cure, 10 sec.                                                        10 sec.                                          C    Example 2 800 cps 2.4   cure, 10 sec.                                                                          cure, 10 sec.                           D    Example 2 143 cps 2.9   no cure, cure, 10 sec.                                                        10 sec.                                          ______________________________________                                    

EXAMPLE 6

The efficiency of bis(dodecylphenyl)iodonium hexafluoroantimonate as aUV catalyst for thin coatings of epoxy functional silicones applied totypical release substrates may also be evaluated. Coating mixtures ofseveral epoxy functional silicones having 2% by weight of thebis(dodecylphenyl)iodonium hexafluoroantimonate were prepared asdescribed in Example 5 above and were applied as coatings ofapproximately 0.5 mils to super calendared Kraft paper (SCK),polyethylene Kraft (PEK), and Mylar substrates by means of a doctorblade. The coated samples were then irradiated by one H377 UV lamp at adistance of 5 inches from the coated surface until a tack-free coatingwas obtained. The resulting films were then evaluated for theirpotential as release agents by qualitatively determining the films'rub-off, smear, migration, and release characteristics by techniqueswell-known to those familiar with release coating applications.

Rub-off occurs when a silicone coating fails to adhere to the substrateand can be rubbed off in little balls of cured silicone by gentle fingerpressure. Smear is detected in an incompletely cured coating when afinger firmly pressed across the silicone film leaves an obviouspermanent streak. Migration is detected by the Scotch (trademark)cellophane tape test. The coating is considered well cured andmigration-free if a piece of No. 610 Scotch tape will stick to itselfafter having been first firmly pressed into the silicone coating, thenremoved and doubled back on itself. If a silicone coating is shown to bemigration-free by means of the Scotch tape test, it is considered to bea release coating because it adheres to the substrate with an adhesiveforce much greater than the adhesive force between the cured compositionand the released aggressive Scotch tape. These qualitative tests areuniversally employed to ascertain the completeness of cure in siliconepaper release coatings.

All of the sample epoxy functional silicone fluids listed in Table IIcured to smear and migration-free non-adherent surfaces on the threesubstrates (SCK, PEK and Mylar) tested within approximately 10 to 15seconds exposure from the single UV lamp when catalyzed with the 2% byweight crude iodonium salt of formula (II). Furthermore, it has beenfound that rub-off of cured coatings on SCK can be minimized if thesubstrate is mildly warmed. However, since mercury lamps used in UV cureoperations generate considerable heat, rub-off from cellulosicsubstrates will not be a problem under these conditions. In thefollowing table, "Synthesis" again refers to the method by which theepoxy functional silicone fluid was prepared.

                  TABLE II                                                        ______________________________________                                                      Wt. % Cure Speed in Sec.                                        Trial                                                                              Synthesis Viscosity                                                                              Epoxy SCK    PEK   Mylar                              ______________________________________                                        A    Example 1 782 cps  10.8  10-15  10-15 10-15                              B    Example 3 950 cps  15.3  10-15  5     10-15                              C    Example 3  95 cps  12.2  No cure                                                                              15    15                                                               (smear)                                         ______________________________________                                    

The low viscosity of the silicone blend used in Trial C allowed it tosoak into the surface of the SCK paper to the extent that a good curewas prevented. All of the samples tested displayed excellent cure on PEKwithout the need of adhesion promoters. This characteristic behavior ofthis system is quite significant because standard heat-cured solventlesssilicone release agents cannot be cured on most polyethylene orpolypropylene films at oven temperatures sufficiently low to preventdestructive degradation of these substrates. Brief exposure toultraviolet radiation, however, cures the epoxy silicone releasecompositions herein described without affecting the substrates.

Further UV cure evaluations may be accomplished by using a P.P.G. Model1202 AN Ultraviolet Processor. This P.P.G. device utilizes two Hanoviamedium pressure mercury vapor ultraviolet sources delivering 200 wattsper square inch focused power to the irradiated surfaces. Samples to beexposed to UV radiation are affixed to a rigid carrier board and thenpassed under the lamps on a conveyor belt which operates at variablespeeds from approximately 5 to 500 feet per minute. Since the focusedlamp radiation is confined to an area about 6 inches wide on the movingconveyor belt, exposure times will vary from approximately 0.06 to 6seconds for any individual pass under the lamps.

EXAMPLE 7

The following example further illustrates the cure behavior of the epoxyfunctional silicone fluids of the present invention. Coating baths ofthe candidate fluids were catalyzed with 1% by weight ofbis(4-dodecylphenyl)iodonium hexafluoroantimonate. These fluids werehand-coated with a doctor blade onto 4 by 10 inch sections of PEK, SCKor Mylar which had previously been affixed to a carrier board. Thecoated substrates were then loaded onto the moving conveyor and exposedto the UV lamps of the P.P.G. processor for varying exposure times,depending on the line speed employed. Following exposure, the coatedfluids were qualitatively examined for degree of cure by determining thepresence or absence of smear, migration, and rub-off as described above.Because the P.P.G. UV processor delivers considerably more radiantenergy to trial samples than the single H3T7 UV bulb utilized in earlierexamples, the cure times observed for these experimental releasecompositions are much lower than those reported above. Table III depictsthe cure time in seconds for epoxy functional silicone fluids containingvarious amounts of epoxy functionality as a weight percent of4-vinylcyclohexene oxide. In the Table, the heading "Weight % Vinyl"refers to the small amount of vinyl functional dimethylsilicone fluidswhich may be added to the vinyl epoxide during the hydrosilationreaction of the hydrogen functional precursor fluids. It has been foundthat the addition of a small amount of vinyl functional silicone fluidis an excellent way to obtain low viscosity products. It can be seenfrom the table that the viscosity of the epoxy functional fluidsprepared as described above is directly dependent upon both the epoxycontent and the degree of pre-crosslinking permitted via the vinylfluid. Viscosities of from approximately 300 to 1,000 centipoise aremost preferred for solventless silicone applications. Exceptionally fastcures are noted on polyethylene substrates when the epoxy content is aslow as 3%. Cure speed on SCK and Mylar was about equal. Thus, it isreadily apparent that the cure rate is directly proportional to theepoxy content and a dramatic increase in cure rates can be seen in trialE where the epoxy content was above 20%. As noted above, there is also acorrelation between cure speed and the degree of pre-crosslinkingintroduced into the epoxy functional silicone intermediate by use ofvinyl functional fluids in the synthesis process. Higher amounts ofthese vinyl functional fluids significantly enhance cure rates.Introduction of these pre-crosslinking materials serve to minimize thedilution of cure performance which would otherwise result from loweringthe amount of epoxy present in these compositions.

                  TABLE III                                                       ______________________________________                                        Wt. %      Wt. %             Cure Time in Seconds                             Sample                                                                              Epoxy    Vinyl   Viscosity                                                                             SCK   PEK   Mylar                              ______________________________________                                        A     7.8      2.1     670 cps 1.0   0.2   1.0                                B     6.1      0       280 cps 1.5   0.4   1.5                                C     5.8      2.1     350 cps 1.0   0.2   1.0                                D     5.75     2.4     675 cps 1.5   0.4   2.0                                E     26.0     0       1200 cps                                                                              <0.1  <0.1  <0.1                               F     3.4      4.6     312 cps 1.5   0.6   3.0                                G     2.9      5.8     800 cps 3.0   1.0   5.0                                ______________________________________                                    

EXAMPLE 8

In order to better assess the utility of these epoxy functional siliconecompositions as paper release agents, quantitative measurements of therelease characteristics of cured coatings of these materials when incontact with common aggressive adhesives can also be determined.Candidate compositions were prepared according to the synthesisdescribed in Examples 3 and 4 above. Thin coatings of these compositionswere catalyzed with 1% by weight of bis(4-dodecylphenyl)iodoniumhexafluoroantimonate and were coated onto SCK with a doctor blade andthen exposed to ultraviolet light for 1.5 seconds within the P.P.G.processor. Two 1×6 inch strips of Curity Wet-Pruf Adhesive Tape (No.3142) were then applied to the cured epoxy silicone coatings and pressedinto place by two passes with a 4.85 pound rubber roller. An identical1×6 inch piece of tape was firmly affixed to the top of one of the tapesalready in contact with the silicone layer. This layer was a blank orcontrol. The laminate so prepared was then aged at 140° F. for 20 hoursin an oven. Following removal from the oven, test laminates were allowedto cool to room conditions of 74° F. and 50% relative humidity.

The control tape was carefully removed from the back of the test tapeand was affixed to a clean stainless steel "Q" panel. The force requiredto remove the test strips from the silicone surface was next ascertainedby pulling the tape from the cured epoxy-silicone surface at 12 inchesper minute on an Instron test device, and the required force wasrecorded in grams. Following removal of the test strips from thesilicone release surfaces, one of the two test strips was affixed to thestainless steel "Q" panel adjacent to the control tape. The forcerequired to remove both the control and the delaminated test tapes fromthe stainless steel surface was recorded. The percent of subsequentadhesion (%SA) can be calculated by comparing the recorded results fortest and control strips, where percent SA equals the test divided by thecontrol. A 90% SA or better demonstrates that no significant migrationof silicone onto the adhesive took place. This is a quantitative versionof the Scotch tape migration test described earlier. Test results forvarious samples correlating percent SA and percent epoxy content may befound in Table IV where again percent epoxy refers to the epoxyfunctionality in the form of 4-vinylcyclohexene oxide.

                  TABLE IV                                                        ______________________________________                                                            Release, in grams                                         Sample  % Epoxy     for 6 trials % SA                                         ______________________________________                                        A       2.9         20-45         90                                          B       3.4         20-40         90                                          C       5.8         25-40        100                                          D       7.8         35-60        100                                          E       11.0         70-100      100                                          F       26.0        350-400      100                                          G       37.0        350-500      100                                          ______________________________________                                    

By comparison, standard solvent dispersed silicone release agents willtypically provide release of 40 to 70 grams under these conditions, soit is apparent that the epoxy functional dimethylsilicone fluids of thepresent invention can be cured with ultraviolet light to formnonadherent surfaces with acceptable release performance when the epoxycontent is limited to about 8% or less. Of course, applications in whichhigher controlled release is desired would find high epoxy compositionsuseful. The present invention makes a wide range of releasecharacteristics available by simple manipulation of the epoxy content inthe epoxy functional silicones herein-described.

The adhesion to a substrate for UV cured paper release compositions canbe improved with the addition of small amount ofβ-(3,4-epoxycyclohexyl)ethyltrimethoxy silane, having the followingformula, ##STR4## during the hydrosilation addition of the vinylfunctional epoxides to the Si-H precursor fluids as described in Example7 above. Addition of this epoxy compound will particularly improveadhesion of the cured epoxy-silicone films to cellulosic substrates.

Thus, a new epoxy functional UV curable silicone paper release fluid canbe synthesized in the following fashion:

EXAMPLE 9

60 grams of dimethylvinyl-chain-stopped linear polydimethylsiloxanefluid having a viscosity of 220 centipoise is combined with 30 grams of4-vinylcyclohexene oxide and 5 grams ofβ-(3,4-epoxycyclohexyl)ethyltrimethoxy silane along with 0.05 grams ofplatinum catalyst. These materials are dissolved in 400 grams hexane ina two-liter flask. Added to the flask is 300 grams of a dimethylhydrogenchainstopped polydimethylmethylhydrogensiloxane copolymer containing atotal of 4.3 weight percent of Si-H units. This material is slowly addedto the stirring hexane solution over a 40-minute period. Following thisaddition, the complete reaction mixture is refluxed at 73° C. for 2hours and 10 grams of normal hexene is added as a scavenger. Full refluxis resumed for 16 additional hours. Stripping off of the hexane solventand the excess hexene at 80° C. under vacuum left a clear viscous fluidwith a viscosity of 600 centipoise which contained 7.6 weight percentepoxide (in the form of 4-vinylcyclohexene oxide) and infrared analysiscould not detect any unreacted Si-H groups.

Another sample was prepared precisely as described above, however, noβ-(3,4 epoxycyclohexyl)ethyltrimethoxy silane was included in thissynthesis. These two products were catalyzed with 1.5% by weightbis(4-dodecylphenyl)iodonium hexafluoroantimonate and were then coatedonto 40 pound SCK paper with a doctor blade and cured with ultravioletlight in the P.P.G. UV processor. The composition including the silane(IV) could be cured to a smear and migration-free adhesive coatingdisplaying little tendency to rub off the paper substrate in about 0.15seconds of UV exposure. By contrast, the identical fluid lacking thesilane coupling agent (IV) required a minimum of 1.0 seconds UV exposureto overcome unsatisfactory rub-off of the otherwise cured coatings fromSCK substrates. Thus, the use of additive (IV) permits 5 to 10 times theline speed otherwise required for reasonable cure.

EXAMPLE 10

Additional quantitative measurements of the release characteristics ofUV cured coatings of these epoxy functional silicone compositions havebeen obtained. The composition is prepared in a fashion alalogous toExample 9 above and had a viscosity of 500 centipoise and an epoxycontent of 7.3%. Again, 1.5% by weight of the iodonium salt catalyst wasadded to the composition. Thin coatings were applied to 40 pound SCKpaper by means of a doctor blade and were cured to a smear andmigration-free adhesive surface with 0.15 seconds exposure toultraviolet light as described in Example 7. After the cured siliconecoatings were aged at room temperature for 2 hours, a 10 mil thick layerof Monsanto GMS-236 (Gelva 263) wet acrylic adhesive was applied on topof the silicone layer and then cured for 15 minutes at room temperatureand additionally for 15 minutes at 150° F. A second sheet of SCK stockwas then firmly pressed onto the adhesive layer. Lamina so prepared werecut into 2×9 inch strips and aged at 75° F. or at 140° F. Releasetesting of these laminates was accomplished immediately after theirpreparation and at regular time intervals upon aging by pulling theSCK/adhesive lamina from the SCK/silicone lamina at an angle of 180° at400 inches per minute. The force required to separate the two lamina wasrecorded in grams. The results of this test are disclosed in Table V.

                  TABLE 1                                                         ______________________________________                                        Laminate                                                                              Release in grams for                                                  Age     Samples Aged at 75° F.                                                                 Samples Aged at 140° F.                        ______________________________________                                        Initial 30              30-35                                                 1 Day   30              40-60                                                 1 Week  40              50-60                                                 2 Weeks 30-40           45-55                                                 4 Weeks 40-55           50-65                                                 ______________________________________                                    

EXAMPLE 11

The versatility of the UV curable epoxy functional silicone releasecompositions of the present invention can be demonstrated by utilizing awide range of common adhesives. A batch of epoxy-silicone fluid wasprepared by combining 610 grams of a dimethylvinyl chain-stoppedpolydimethylsiloxane fluid having a viscosity of 150 centipoise with 305grams of 4-vinylcyclohexene oxide and 50 grams of β-(3,4epoxycyclohexyl)ethyltrimethoxysilane. These materials were mixed with0.2 grams of platinum catalyst as described above and were dissolved in4 kilograms of hexane. Slowly added to the stirring solution at 25° C.were 3 kilograms of dimethylhydrogen chainstoppedpolydimethyl-methylhydrogensiloxane copolymer having a viscosity of 130centipoise and containing 4.1% methylhydrogensiloxy units. Following theaddition, the reaction mixture was refluxed at 73° C. for 4 hours andthen cooled to below 70° C. whereupon 100 grams of normal hexene wereadded and refluxing was continued for 15 hours to complete the reaction.Following the reflux, the hexane solvent and the unreacted hexene werestripped off under 30 millimeters Hg vacuum at 100° C. affording a clearamber colored fluid product having a viscosity of 550 centipoise andcontaining approximately 7.5% epoxy functionality (in the form of4-vinylcyclohexeneoxide) and infrared analysis detected no unreactedmethylhydrogen functionality remaining. As noted above, small amounts (1to 2% by weight) of β-(3,4 epoxycyclohexyl)ethyltrimethoxy silane addedto these compositions aid in their cure and their adhesion to papersubstrates. Note, however, that the use of this substance is notessential to the performance of the paper release product although it isa useful additive.

100 parts of the above-described epoxy functional silicone fluid weremixed with two parts of bis(4-dodecylphenyl)iodoniumhexafluoroantimonate until a uniform dispersion of the catalyst withinthe silicone was obtained. The catalyzed composition was then coatedonto an 18-inch wide roll of low density polyethylene coated Kraft paperby means of a three-roll offset gravure pilot quarter. Those skilled inthe art will recognize that such offset gravure equipment isparticularly well suited for depositing even thin films of solventlesssilicones on paper substrates for release applications. A single 18-inchlong Hanovia medium pressure mercury vapor ultraviolet lamp provided 300watts per square inch of focused radiation and was mounted above themoving substrate within three feet of the coating head so that the UVlight was focused across the entire width of the silicone coated paper.Smear and migration-free cured coatings were obtained on the PEKsubstrate at line speeds up to 100 feet per minute. These line speedsprovided UV exposures of approximately 0.05 seconds.

It should be noted that low density polyethylene coated Kraft substratesare very sensitive to heat and conventional thermally-cured siliconerelease coatings cannot be cured on these materials. However, the UVcured compositions described herein are particularly well suited forthis application. In order to evaluate the cured coatings releaseperformance, a wide range of silicone depositions were obtained at aline speed of 75 fpm. The cured coatings on the PEK substrate werestored at 0° to 30° C. for a week, and lamina were prepared utilizingthree common adhesives. The release characteristics of theseepoxy-silicone coatings were measured in grams as described previously.The results are summarized in Table VI.

                  TABLE VI                                                        ______________________________________                                        Silicone                                                                      Deposition,    Release, Grams                                                 Sample  Pounds/Ream                                                                              M-12*     A-40** Gelva***                                  ______________________________________                                        1       0.36        80-100   110-140                                                                              55-70                                     2       0.24       110-120   160-200                                                                              60-80                                     3       0.47       70-95     110-135                                                                              50-60                                     4       0.57       65-85      90-120                                                                              40-55                                     ______________________________________                                         *M-12 Removable SBR Adhesive (Dennison Mfg. Co.)                              **A40 Permanent SBR Adhesive (Dennison Mfg. Co.)                              ***Gelva 263 Acrylic Adhesive (Monsanto)                                 

Higher release values were noted for the lightest silicone depositions.These values did not significantly change after two weeks acceleratedaging at 120° F. As noted above, release measurements falling below 100grams versus the aggressive Gelva adhesive are regarded as premiumrelease products.

What is claimed as new and desired to be protected by Letters Patent ofthe United States is:
 1. An ultraviolet-curable epoxy functionalsilicone intermediate fluid composition comprising a pre-crosslinkedepoxy functional dialkyl epoxy chainstopped polydialkyl-alkyl epoxysiloxane copolymer silicone fluid which comprises the reaction productof:(a) a vinyl- or allylic- functional epoxide; (b) a vinyl functionalsiloxane cross-linking fluid having a viscosity of approximately 1 to100,000 centipoise at 25° C.; (c) a hydrogen functional siloxaneprecursor fluid having a viscosity of approximately 1 to 10,000centipoise at 25° C.; and (d) an effective amount of precious metalcatalyst for facilitating an addition cure hydrosilation reactionbetween said vinyl functional cross-linking fluid, said vinyl functionalepoxide, and said hydrogen functional siloxane precursor fluid.
 2. Acomposition as in claim 1, wherein the vinyl- or allylic- functionalepoxide is a cycloaliphatic epoxy compound.
 3. A composition as in claim2, wherein the cycloaliphatic epoxy compound is selected from the groupconsisting of 4-vinylcyclohexeneoxide, vinylnorbornenemonoxide, anddicyclopentadienemonoxide.
 4. A composition is in claim 1, wherein theprecious metal catalyst is a metal complex and the metal is selectedfrom the group consisting of ruthenium, rhodium, palladium, osmium,irridium and platinum.
 5. A composition as in claim 1, wherein saidvinyl functional siloxane cross-linking fluid is selected from the groupconsisting of dimethylvinyl chainstopped linear polydimethylsiloxane,dimethylvinyl chainstopped polydimethyl-methylvinyl siloxane copolymer,tetravinyltetramethylcyclotetrasiloxane andtetramethyldivinyldisiloxane.
 6. A composition as in claim 1, whereinsaid hydrogen functional siloxane precursor fluid is selected from thegroup consisting of tetrahydrotetramethylcyclotetrasiloxane,dimethylhydrogen chainstopped linear polydimethylsiloxane,dimethylhydrogen chainstopped polydimethyl-methylhydrogen siloxanecopolymer and tetramethyldihydrodisiloxane.
 7. A composition as in claim1, further comprising an effective amount ofβ-(3,4-epoxycyclohexyl)ethyltrimethoxy silane for improving the adhesionof the composition to a substrate.
 8. An ultraviolet-curable epoxyfunctional silicone intermediate fluid composition as in claim 1,further comprising bis (4-dodecylphenyl) iodonium salt effective forcatalyzing an ultraviolet light initiated cure reaction of saidintermediate fluid.